This way of thinking allows us to bring some additional nuance to the approach to causality adopted in the process matrix framework. As we have noted, this approach largely identifies causal influences with signalling, or at least uses signalling as a proxy for causation, whereas most people consider that signalling is at best a sufficient condition for the presence of a causal relation[1]}. However, the understanding that causal ordering is related to consistency requirements allows us to avoid presupposing the association of causation with signalling, and rather to derive it from more fundamental considerations. That is, suppose we accept that ordinary causal phenomena arise from an underlying causal order together with a choice of direction. Then recall that consistency requirements impose conditions only on signalling processes, not on no-signalling ones. It follows that causal order, and hence causal phenomena, will typically be associated with signalling processes and not with no-signalling ones, so the association of `causation' with `signalling' in this framework can thus be retrospectively justified.
